1. Field of the Invention
This invention relates to the field of polymer blends and, more particularly, to blends of polyvinyl chloride, vinyl acetate-ethylene copolymer and inorganic particulate filler.
2. Description of the Prior Art
It is well known that relatively few polymer-polymer blends have useful properties due to their incompatibility. Even useful polymer blends, such as those of nitrile rubber in styrene-acrylonitrile copolymer to increase impact strength, have been greatly improved by substituting rubber styrene-acrylonitrile graft copolymers for the nitrile rubber to provide superior impact resistance. These well known compositions are now generally referred to as the ABS (acrylonitrile-butadiene-styrene) resins.
Techniques other than that of graft polymerization have been employed for introducing compatibility in polymer blends, or alloys. Thus, for example, as described in U.S. Pat. No. 3,906,057, a block copolymer which combines blocks of two homopolymers in a single macromolecule will compatibilize a blend of the homopolymers when added in amounts of about 5-40 weight parts per hundred parts of blend. Similarly, U.S. Pat. No. 3,485,777 describes the compatibilization of polymer blends by the addition of a graft copolymer having molecular segments of solubility characteristics similar to the solubility characteristics of the blended component polymers. Variations of these compatibilization techniques include coupling polymer components in situ with coupling agents as described in U.S. Pat. No. 3,645,939.
These methods of obtaining compatibilization in polymer blends are of limited usefulness since they each depend upon some special additive and extensive working or a chemical reaction to achieve the result desired. Accordingly, attempts have been made in the past to obtain compatibilized polymer blends by merely blending the component polymers using simple known and conventional procedures. A number of polymer alloys containing ethylene-vinyl acetate copolymer or ethylene-vinyl acetate-vinyl alcohol terpolymer and one or more other polymers are known. U.S. Pat. Nos. 3,125,545 and 3,517,083 describe improved impact strength polymer blends based on polyvinyl chloride and ethylene-vinyl acetate copolymer. Not surprisingly, these blends, which are prepared by conventional simultaneous mixing of the resin components, have been found to be unstable. In this connection, U.S. Pat. No. 3,758,661 may be noted for its recognition that copolymers of alpha-olefins such as ethylene-vinyl acetate resin possess poor compatibility with resins such as polyvinyl chloride. U.S. Pat. No. 3,156,666 describes compatible blends of ethylene-vinyl acetate copolymer, an alpha-olefin polymer or copolymer and particulate silica filler. The blending procedure contemplates preparing a pre-blend of either resin with the silica filler. Blends containing rigid polyvinyl chloride resin are neither mentioned nor suggested. U.S. Pat. No. 3,278,645 describes the blending of chlorinated polyethylene pre-blended with pigment, and ethylene-vinyl acetate copolymer. U.S. Pat. No. 3,283,025 describes a polymer blend of polyvinyl chloride containing at least 80 weight percent vinyl chloride and optionally having incorporated therein minor quantities of a copolymerizable monomer such as acrylonitrile, together with 2 to 40 parts by weight of said polyvinyl chloride of an ethylene-vinyl acetate copolymer containing 2 to 65 weight percent vinyl acetate and 3 to 10 parts by weight of said polyvinyl chloride of a chlorinated polyethylene containing 35 weight percent chlorine. No mention is made of the use of a styrene-acrylonitrile copolymer in the aforesaid polymer blends. U.S. Pat. No. 3,322,858 describes multicomponent polymer blends containing vinyl chloride grafted copolymers of up to 50 weight percent ethylene-vinyl acetate copolymer (with the working examples indicating a preference for substantially smaller quantities of ethylene-vinyl acetate copolymer in the graft resin), a chlorinated polyethylene resin and a styrene acrylonitrile copolymer as a processing aid. U.S. Pat. No. 3,549,727 discloses polymer blends containing ethylene-vinyl acetate-vinyl alcohol terpolymer. The use of polyvinyl chloride, chlorinated polyethylene and/or styrene-acrylonitrile copolymer are neither disclosed nor suggested. U.S. Pat. No. 3,644,577 describes polymer blends containing 60 to 95 weight percent polyvinyl chloride and 40 to 5 weight percent of a nitrile copolymer such as styrene-acrylonitrile copolymer. The blends may also contain as an optional ingredient an impact modifier such as an ethylene-vinyl acetate copolymer. The characteristics of the polymers disclosed in this patent are largely those of polyvinyl chloride reflecting the dominant presence of this resin in the blends. U.S. Pat. No. 3,758,661 is illustrative of a two component blend containing a copolymer of an alpha-olefin and a copolymerizable monomer therewith, e.g., ethylene-vinyl acetate copolymer, and a resin having poor compatibility with the olefinic resin such as styrene-acrylonitrile copolymer or polyvinyl chloride. U.S. Pat. No. 3,960,986 describes impact-resistant molding compositions containing 20 to 80 percent polyvinyl chloride, 19.5 to 75 weight percent of a vinyl chloride graft copolymer of ethylene and vinyl acetate and 0.5 to 5.0 weight percent ethylene-vinyl acetate copolymer. The incorporation of nitrile-containing copolymer such as styrene-acrylonitrile copolymer is not mentioned in this patent. U.S. Pat. No. 4,141,936 disclosed compatibilized blends of certain kinds of vinyl acetate-ethylene copolymers and/or ethylene-vinyl acetate-vinyl alcohol terpolymers, styrene-acrylonitrile copolymer, polyvinyl chloride or chlorinated polyethylene, and optionally, small quantities of filler.